Patent GB-613549-A (GB)
Title: Improvements in or relating to the control of alternating current motors for drivingwinder equipment
IPC: H02P3/24
Filed: 1946-05-17
Abstract: 613,549. Control of A.C. motors; controllers. GENERAL ELECTRIC CO., Ltd., and MAER, C. A. May 17, 1946, No. 14986. [Class 38 (iii)] One of the windings, preferably the stator winding of a wound rotor induction motor 1 is supplied with direct-current or low-frequency alternating-current during dynamic braking and the power generated in the other winding is absorbed in a resistance, one control member 16 being arranged to control motoring, and possibly reverse current braking, and a second control member 17 is adapted to apply and control both mechanical and dynamic braking, the arrangement being such that the initial movement of the member 17 from its " off " position is adapted to apply dynamic braking which is controlled by further movement of that member away from such position, and additional movement beyond a certain position is adapted to apply mechanical braking and terminate dynamic braking. The degree of dynamic braking 'is preferably simultaneously controlled by means of the rotor resistance 3 and of the direct-current or low-frequency excitation of the stator winding. In a preferred arrangement, dynamic braking is discontinued after mechanical braking has been applied. The system comprises a number of interlock switches to prevent simultaneous operation of various contactors therein. Movement of a motoring controller 10 to a "forward" position engages fingers 25 and 26 to energize a coil 43 of a pilot contactor 12 which closes contacts 59 to supply direct-current, through a rectifier 49, to a coil 46 of a main forward contactor 8. The stator winding of the motor 1 is energized, speed control being effected by means of the liquid controller 3. Movement of the controller 10 to a " reverse " position interconnects the fingers 25 and 27 to energize contactors 13 and 9. When the braking controller 15 is moved to bridge fingers 36 and 37, coils 42 and 45 of contactors 11 and 14 are energized through contacts 32 and 33, which are closed only in the neutral position of the controller 10. The contactor 19 is closed to apply direct-current excitation to the motor stator winding from a motor-generator set 20-21. The lever 16 (see Fig. 2) is adapted to turn a shaft 91 which is coupled to the controller 10 and an assister gear arrangement 18 which drives the liquid controller 3. The lever 17 is linked through a member 92 with a mechanical brake which is applied when the lever passes the half-way position, a weight 93, which is normally held-off by a solenoid 94, being provided to apply emergency braking. The controller 15 is so constructed and so operated, through a rachet and cam device 101, that the contacts 36 and 37 are only closed when the lever 17 moves from the " off " position to just past the " half-way " position, and not when the lever is used to control mechanical braking or is being returned to the " off position. The lever 17 is linked with the liquid controller 3 through a lever 96 having cam surfaces 97 engageable by a pin 98 which is carried on the lever. The lever 96 is biassed by a weight 99 in a direction corresponding to maximum liquid resistance. The pin 98 rides off the cam surfaces 97 when the lever 17 moves beyond the " half-way " position, allowing the liquid controller to be moved back to the maximum-resistance position. A pivoted catch is provided to allow the pin to re-engage the cam surfaces when the lever is moved towards its " off " position after mechanical braking. The cam surfaces 97 are so shaped that the rate of reduction of rotor resistance is made to conform to a desired characteristic. The lever 17 is also linked with a regulating resistance 24 in the field-winding circuit of the generator 21, so as to co-ordinate the control of the direct-current excitation and of the rotor resistance. The assister gear 18 may be arranged so that, during motoring, initially it cuts-out the resistance of the liquid controller 3 rapidly, and thereafter removes the resistance at a slower rate. During dynamic braking, the whole resistance is removed at a slow rate due to the effect of a solenoid 82 which is energized through a contact of the switch 19, this solenoid controlling the operation of a valve in the exhaust side of an oil pressureoperated piston forming part of the assister gear. The system may comprise an interlock contactor 73 which prevents operation of either contactor 8 or 9 until the other contactor has opened and any arcing at the contacts thereof has terminated.